Scanning optical apparatus and method for manufacturing reflection member

ABSTRACT

A scanning optical apparatus includes: a deflection unit configured to deflect a light flux from a light source in a main scanning direction; an incident optical system configured to introduce the light flux from the light source to the deflection unit; a condensing optical system configured to condense the light flux from the deflection unit onto a scanned surface; and a reflection member arranged in a light path of the light flux deflected in the main scanning direction by the deflection unit and configured to reflect a part of the deflected light flux. The reflection member has a reflection surface configured to reflect the deflected light flux, a first end surface formed in the main scanning direction, and a second end surface formed in a sub-scanning direction perpendicular to the main scanning direction, and the second end surface has a higher degree of corrosion resistance than the first end surface.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a scanning optical apparatus and amethod for manufacturing a reflection member, which are suitable for animage forming apparatus having an electrophotographic process, such as alaser beam printer (LBP), a digital copying machine, or a multifunctionprinter.

2. Description of the Related Art

There have been proposed various types of scanning optical apparatusesfor a laser beam printer (LBP), a digital copying machine, or amultifunction printer, which has an electrophotographic process. Such ascanning optical apparatus converts a light flux, which has beenoptically modulated and emitted from a light source unit in response toan image signal, into a parallel light flux by a collimator lens andperiodically deflects the parallel light flux by an optical deflectionunit including a rotating polygon mirror. The deflected light flux isthen condensed in a spot shape on a surface of a photosensitiverecording medium (photosensitive drum) by a condensing optical system(imaging optical system) having fθ characteristics, and the spot-shapedlight flux optically scans the surface to perform image recording.

It has recently been requested, in the case of a laser beam printer, andthe like, that high-speed printing be possible, or high-precisionprinting be obtained. In either case, the number of scanning per unittime needs to be increased. Such a request has been met until now byincreasing the number of surfaces of the rotating polygon mirror or byincreasing the number of rotations. These methods have a problem in thatthe rotating polygon mirror becomes larger and rotates at a high speed,that is, the load on the driving motor of the optical deflection unitincreases, as well as problems of temperature rise, noise, and increasedoverall size of the apparatus.

In an attempt to reduce the load on the optical deflection unit, therehave been proposed various types of scanning optical apparatusesemploying a multi-beam scanning system, which increase thelight-emitting points (light-emitting units) of the semiconductor laseras a light source unit and scan the scanned surface using a plurality oflight fluxes simultaneously.

It has been generalized, in such a multi-beam scanning system, toprovide a synchronous detection optical system and a synchronousdetection light-receiving element, as also known in the single-beamscanning system, in order to accurately perform the printing/writingtiming of the scanned beam (Japanese Patent Application Laid-open No.H08-179230). In Japanese Patent Application Laid-open No. H08-179230, asynchronous detection mirror is arranged to bend the synchronousdetection light flux, and the fθ lens and the light-collecting lens areintegrated, so as to reduce the interval between the printing light fluxat the outermost angle and the synchronous detection light flux(referred to as gap G in the document).

A synchronous detection mirror employed for such synchronous detectionis arranged near the scanning light flux for printing, in an attempt tomake the apparatus smaller in the main scanning direction, and thereforehas a smaller size (in general, about 10 mm×10 mm) than a mirrorconfigured to reflect the scanning light flux for printing. Conventionalmethods for manufacturing such a synchronous detection mirror includelarge-size deposition and post-cutting in longitudinal and transversedirections.

This will be described in detail with reference to FIGS. 5A to 5C.Referring to FIG. 5A, a glass plate 961 (thickness: about 1.8 mm) ofabout 125 mm×125 mm, for example, is cleaned sufficiently, and a vacuumdeposition machine is used to deposit a reflection coating 962 as ametallic coating including aluminum or an aluminum-containing alloy. Aprotection film 963 having SiO₂ or the like as a main component is thendeposited on the reflection coating 962. Thereafter, as illustrated inFIG. 5B, known scribe cutting is employed to bend and cut the glassplate 961 into a desired piece size (for example, 10 mm×10 mm) in thelongitudinal and transverse directions. The sectional surface (FIG. 5C)obtained by scribe cutting is generally susceptible to burring, so thatthe cut surface or its angled portion is commonly grinded orlight-chamfered.

Another manufacturing method includes pre-cutting in the longitudinaland transverse directions into a piece size and post-deposition, thatis, a glass plate is initially cut into a piece size of 10 mm×10 mm,followed by deposition. This method requires a great effort to set theglass plate of a piece size in a vacuum deposition machine, resulting ina high cost. Furthermore, the light piece glass plate can be easilydisplaced inside the vacuum deposition machine by small impact orvibration, making it difficult to obtain a uniform film. Therefore,synchronous detection mirrors for synchronous detection are generallymanufactured according to the above-mentioned method of large-sizedeposition and post-cutting in longitudinal and transverse directions.

SUMMARY OF THE INVENTION

A scanning optical apparatus according to the present inventionincludes: a deflection unit configured to deflect a light flux from alight source in a main scanning direction; an incident optical systemconfigured to introduce the light flux from the light source to thedeflection unit; a condensing optical system (imaging optical system)configured to condense the light flux from the deflection unit onto ascanned surface; and a reflection member arranged in a light path of thelight flux deflected in the main scanning direction by the deflectionunit and configured to reflect a part of the deflected light flux. Thereflection member has a reflection surface configured to reflect thedeflected light flux, a first end surface formed in the main scanningdirection, and a second end surface formed in a sub-scanning directionperpendicular to the main scanning direction, and the second end surfacehas a higher degree of corrosion resistance than the first end surface.

Also, in a scanning optical apparatus including: a deflection unitconfigured to deflect a light flux from a light source in a mainscanning direction; an incident optical system configured to introducethe light flux from the light source to the deflection unit; acondensing optical system configured to condense the light flux from thedeflection unit onto a scanned surface; and a reflection member arrangedin a light path of the light flux deflected in the main scanningdirection by the deflection unit and configured to reflect a part of thedeflected light flux, a method for manufacturing a reflection member ofthe optical scanning apparatus includes: cutting a reflection opticalsubstrate in a first cutting direction corresponding to a directionparallel with a sub-scanning direction perpendicular to the mainscanning direction and obtaining a first optical member piece of arectangular shape elongated in the first cutting direction; forming areflection coating on a reflection optical surface of the first opticalmember piece; and cutting the first optical member piece in a secondcutting direction corresponding to a direction parallel with the mainscanning direction and obtaining a second optical member piece as thereflection member.

Also, in a scanning optical apparatus including: a deflection unitconfigured to deflect a light flux from a light source in a mainscanning direction; an incident optical system (2, 3, 4) configured tointroduce the light flux from the light source to the deflection unit; acondensing optical system (6) configured to condense the light flux fromthe deflection unit onto a scanned surface; and a reflection member (9)arranged in a light path of the light flux deflected in the mainscanning direction by the deflection unit and configured to reflect apart of the deflected light flux, a method for manufacturing the opticalscanning apparatus includes: cutting a reflection optical substrate in afirst cutting direction corresponding to a direction parallel with asub-scanning direction perpendicular to the main scanning direction andobtaining a first optical member piece (930) of a rectangular shapeelongated in the first cutting direction; forming a reflection coatingon a reflection optical surface of the first optical member piece (930);cutting the first optical member piece (930) in a second cuttingdirection corresponding to a direction parallel with the main scanningdirection and obtaining a second optical member piece (9′) as thereflection member; and embedding the second optical member piece in ahousing of the scanning optical apparatus.

Also, in a scanning optical apparatus including: a deflection unitconfigured to deflect a light flux from a light source in a mainscanning direction; an incident optical system configured to introducethe light flux from the light source to the deflection unit; acondensing optical system configured to condense the light flux from thedeflection unit onto a scanned surface; and a reflection member arrangedin a light path of the light flux deflected in the main scanningdirection by the deflection unit and configured to reflect a part of thedeflected light flux, another method for manufacturing a reflectionmember of the scanning optical apparatus according to the presentinvention includes: forming a reflection coating on a reflection opticalsurface of a reflection optical substrate; cutting the reflectionoptical substrate, on which the reflection coating has been formed, in afirst cutting direction corresponding to a direction parallel with asub-scanning direction perpendicular to the main scanning direction andobtaining a first optical member piece of a rectangular shape elongatedin the first cutting direction; applying a corrosion inhibitor to an endsurface of the first optical member piece cut in the first cuttingdirection; and cutting the first optical member piece in a secondcutting direction corresponding to a direction parallel with the mainscanning direction and obtaining a second optical member piece as thereflection member.

Also, in a scanning optical apparatus including: a deflection unitconfigured to deflect a light flux from a light source in a mainscanning direction; an incident optical system (2, 3, 4) configured tointroduce the light flux from the light source to the deflection unit; acondensing optical system (6) configured to condense the light flux fromthe deflection unit onto a scanned surface; and a reflection member (9)arranged in a light path of the light flux deflected in the mainscanning direction by the deflection unit and configured to reflect apart of the deflected light flux, another method for manufacturing theoptical scanning apparatus includes: forming a reflection coating (942)on a reflection optical surface of a reflection optical substrate (941);cutting the reflection optical substrate (941), on which the reflectioncoating has been formed, in a first cutting direction corresponding to adirection parallel with a sub-scanning direction perpendicular to themain scanning direction and obtaining a first optical member piece (943)of a rectangular shape elongated in the first cutting direction;applying a corrosion inhibitor to an end surface (944) of the firstoptical member piece (943) cut in the first cutting direction; cuttingthe first optical member piece (943) in a second cutting directioncorresponding to a direction parallel with the main scanning directionand obtaining a second optical member piece (9′) as the reflectionmember; and embedding the second optical member piece in a housing ofthe scanning optical apparatus.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a main scanning arrangement diagram of a scanning opticalapparatus according to an embodiment of the present invention.

FIG. 1B is a perspective view illustrating major parts of a synchronousdetection reflection optical unit according to an embodiment of thepresent invention.

FIG. 2A is a diagram illustrating each process of a method formanufacturing a synchronous detection mirror as a synchronous detectionreflection optical unit according to a first embodiment.

FIG. 2B is a diagram illustrating each process of a method formanufacturing a synchronous detection mirror as a synchronous detectionreflection optical unit according to a first embodiment.

FIG. 2C is a diagram illustrating each process of a method formanufacturing a synchronous detection mirror as a synchronous detectionreflection optical unit according to a first embodiment.

FIG. 3A is a diagram illustrating each process of a method formanufacturing a synchronous detection mirror as a synchronous detectionreflection optical unit according to a second embodiment.

FIG. 3B is a diagram illustrating each process of a method formanufacturing a synchronous detection mirror as a synchronous detectionreflection optical unit according to a second embodiment.

FIG. 3C is a diagram illustrating each process of a method formanufacturing a synchronous detection mirror as a synchronous detectionreflection optical unit according to a second embodiment.

FIG. 3D is a diagram illustrating each process of a method formanufacturing a synchronous detection mirror as a synchronous detectionreflection optical unit according to a second embodiment.

FIG. 4 is a schematic configuration diagram of an image formingapparatus equipped with a scanning optical apparatus according to anembodiment of the present invention.

FIG. 5A is a diagram illustrating each process of a conventional methodfor manufacturing a synchronous detection mirror as a synchronousdetection reflection optical unit.

FIG. 5B is a diagram illustrating each process of a conventional methodfor manufacturing a synchronous detection mirror as a synchronousdetection reflection optical unit.

FIG. 5C is a diagram illustrating each process of a conventional methodfor manufacturing a synchronous detection mirror as a synchronousdetection reflection optical unit.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

As described above, a conventional reflection member, which isrepresented by a synchronous detection mirror, has a problem in that alight flux, which is deflected in the main scanning direction, isscattered at an end surface through which the light flux passes (endsurface cut in the longitudinal direction). That is, as illustrated inFIGS. 5B and 5C, when the above-mentioned method of large-sizedeposition and post-cutting in longitudinal and transverse directions isemployed, the end portion is curled up, as in the case of end portion965 of the deposition film, at the time of post-cutting. Even whengrinding or light-chamfering is performed to deal with burrs on the cutsurface, the end portion of the deposition film is still curled up.

In this case, the end portion 965 of the deposition film, which has beencurled up, can easily contact external air, including moisture and O₂,and the reflection coating of metallic coating including aluminum or analuminum-containing alloy undergoes oxidation/corrosion (rusting).Particularly, high temperature/high humidity quickens the corrosion,making it difficult to obtain a desired reflection ratio in the area ofthe reflection coating of the corroded metallic coating. In addition,the corrosion starting from the cut surface of the end portion of thereflection member gradually proceeds inwards.

As a result, when up to the part close to the cut surface of thereflection member is used to reflect light fluxes, as in the case ofJapanese Patent Application Laid-open No. H08-179230, the end portionreflection area of the reflection member is corroded due to theinfluence of heat or humidity inside the body of the image formingapparatus, degrading the reflection ratio. This results in a problem inthat the amount of synchronous detection light reaching the synchronousdetection light-receiving element decreases, making sufficientsynchronous detection impossible.

The object of the present invention is to provide a scanning opticalapparatus and a method for manufacturing a reflection member, which canguarantee both compactness and improved durability of the reflectionmember and reduce the cost.

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

First Embodiment Image Forming Apparatus

FIG. 4 is a schematic configuration diagram of an image formingapparatus equipped with a scanning optical apparatus according to anembodiment of the present invention. The image forming apparatus is atandem-type color image forming apparatus having four optical scanningapparatuses arranged in tandem with one another so that imageinformation is recorded on surfaces of photosensitive drums which areimage bearing members. In FIG. 4, reference numeral 60 refers to a colorimage forming apparatus; reference numerals 61, 62, 63, and 64 refer tooptical scanning apparatuses, respectively; reference numerals 71, 72,73, and 74 refer to photosensitive drums as image bearing members,respectively; reference numerals 31, 32, 33, and 34 refer to developingunits, respectively; and reference numeral 51 refers to a conveyingbelt.

In FIG. 4, the color image forming apparatus further includes atransferring unit (not illustrated) configured to transfer a tonerimage, which is obtained by developing an electrostatic latent image onthe photosensitive drums by the developing unit, to a transferredmaterial and a fixing unit (lower left side of FIG. 4) configured to fixthe transferred toner image to the transferred material.

In FIG. 4, respective color signals of R (red), G (green), and B (blue)are input to the color image forming apparatus 60 from an externalapparatus 52 such as a personal computer. These color signals have codedata converted into each image data (dot data) of C (cyan), M (magenta),Y (yellow), and B (black) by a printer controller 53 inside theapparatus.

The image data is input to respective optical scanning apparatus 61, 62,63, and 64. Light beams 41, 42, 43, and 44, which have been modulated inresponse to each image data, are emitted from the optical scanningapparatuses, and the photosensitive surfaces of the photosensitive drums71, 72, 73, and 74 are scanned in the main scanning direction by thelight beams.

The color image forming apparatus according to the present embodimenthas four optical scanning apparatuses 61, 62, 63, and 64 arranged intandem so as to correspond to respective colors of C (cyan), M(magenta), Y (yellow), and B (black). The optical scanning apparatuses61, 62, 63, and 64 record image signals (image information) on thesurfaces of the photosensitive drums 71, 72, 73, and 74 in parallel withone another so that color images can be printed at a high rate.

The color image forming apparatus according to the present embodiment,as described above, has four optical scanning apparatuses 61, 62, 63,and 64 configured to form latent images of respective colors on thesurfaces of the corresponding photosensitive drums 71, 72, 73, and 74using light beams based on each image data. The latent images are thenmulti-transferred to a recording material to form one sheet offull-color image.

The external apparatus 52 can be a color image reading apparatusequipped with a CCD sensor, for example. In this case, the color imagereading apparatus and the color image forming apparatus 60 constitute acolor digital copying machine.

Scanning Optical Apparatus

FIG. 1A is a main scanning arrangement diagram of a scanning opticalapparatus according to an embodiment of the present invention. In thedrawing, reference numeral 1 refers to a laser light source; referencenumeral 2 refers to a light-collecting element; reference numeral 3refers to a cylinder lens; reference numeral 4 refers to a diaphragm;reference numeral 5 refers to a polygon mirror as a deflection unit;reference numeral 6 refers to a condensing lens system including a firstcondensing lens 61 and a second condensing lens 62; reference numeral 7refers to a cover glass; and reference numeral 8 refers to a scannedsurface (photosensitive body). In addition, the collimator lens 2, thecylinder lens 3, and the diaphragm 4 are referred to as apre-deflection-unit optical system or an incident optical system.

Furthermore, the first condensing lens 61 and the second condensing lens62 are condensing lenses made of plastic, and the condensing lens system(condensing optical system, imaging optical system) including these caninclude one lens or at least three lenses. The condensing lens system isconfigured to form an image of the light source on the scanned surface(photosensitive body), specifically form a spot-shaped (spot-shaped,small) light-collecting point of light using the light emitted from thelaser light source.

As will be described later in detail, reference numeral 9 refers to asynchronous detection reflection mirror (BD mirror) as a reflectionmember, which is arranged in the light path as a part of the synchronousdetection unit; reference numeral 10 refers to a synchronous detectioncondensing lens (BD lens); and reference numeral 11 refers to asynchronous detection light-receiving element (BD sensor).

In FIG. 1A, a direction parallel with the paper surface is referred toas a main scanning direction (main scanning section), and a directionperpendicular to this is referred to as a sub-scanning direction(sub-scanning section). Directions of the coordinate system are definedas follows: a direction parallel with the optical axis of the condensinglens system 6 is X-axis direction, a direction perpendicular to thiswhile lying on the paper surface is Y-axis direction, and a directionperpendicular to X-axis and Y-axis (perpendicular to the paper surface)is Z-axis direction.

The laser light source 1 is of an end surface light-emitting type or asurface light-emitting type (VCSEL: vertical-cavity surface-emittinglaser), and is a multi-beam laser having a plurality of light-emittingportions on a single tip. The wavelength λ of emitted light is 650 nm,but the present invention is not limited to this, and infrared light ofwavelength λ=850 nm or blue-ray light of λ=430 nm can also be used.

The divergent light flux emitted from the laser light source 1 iscollected by the light-collecting element 2 and is converted toapproximately parallel light. Although a spherical single lens isillustrated as the light-collecting element 2, the present invention isnot limited to this, and a bonded lens obtained by bonding glassspherical lenses together, a glass-molded lens, or a plastic-molded lenscan also be used. The approximately parallel light emitted by thelight-collecting element 2 is converted to a light flux, which convergesin the sub-scanning direction, by the cylinder lens 3, and is collectednear one reflective deflection surface 51 of the deflection unit 5,thereby forming a line image near the reflective deflection surface 51.

The diaphragm 4 is configured to convert a light flux, which has beenemitted from the cylinder lens 3, to a desired light flux width, and hasan aperture of an elliptical shape, a rectangular shape, or an ovalshape, the shape being determined by the wavelength of the employedlight source, the size of the desired beam spot or its shape. Thediaphragm 4 can be positioned between the light source 1 and thelight-collecting element 2, between the light-collecting element 2 andthe cylinder lens 3, or between the cylinder lens 4 and the deflectionunit 5.

The diaphragm 4 can be installed as two slit members including one slitmember having an edge extending in the sub-scanning direction, forexample, to limit the light flux in the main scanning direction and theother slit member having an edge extending in the main scanningdirection to limit the light flux in the sub-scanning direction.Particularly, when the laser used as the light source has a large numberof light-emitting points, jitter can be reduced by providing a slitmember, which limits the light flux in the main scanning direction, nearthe deflection unit.

Similarly, when the laser used as the light source has a large number oflight-emitting points, uniformity of the printing interval of aplurality of beams can be improved by providing a slit member, whichlimits the light flux in the sub-scanning direction, in a conjugatedposition (approximately between the light source and thelight-collecting element 2) with the scanning lens. Considering such atechnological aspect, a diaphragm split into a plurality of members canbe employed.

The deflection unit 5, which includes a plurality of reflectivedeflection surfaces, is driven rotationally about the rotation axis 52in the direction of arrow A1 in FIG. 1A by a driving system (notillustrated). As a result, a scanning light flux is scanned on thescanned surface 8 in the direction of arrow A2.

The main light ray of the incident light flux introduced into thedeflection unit 5 by the incident optical system is incident in adirection perpendicular to the reflective deflection surface 51 withinthe sub-scanning section. The deflection unit 5 then deflects the lightflux by means of a reflective deflection surface 51, which is drivenrotationally, and introduces the light flux to the condensing lenssystem 6 (an fθ lens, a scanning lens, and also referred to as ascanning optical system).

Next, operations of the condensing lens system 6 will be described. Thecondensing lens system 6 includes two lenses including a firstcondensing lens 61 made of plastic and a second condensing lens 62 madeof plastic. The condensing lens system 6 condenses a light flux, whichhas been deflected by the deflection unit 5, on the scanned surface 8 toform a beam spot, and scans the scanned surface 8 at a constant speed.The first and second condensing lenses 61 and 62, which are made ofplastic, are manufactured by known molding technology: a mold is filledwith a resin, which is cooled and removed from the mold, lowering themanufacturing cost compared with conventional scanning lenses made ofglass lenses.

The condensing lens system 6 is designed by known power arrangement. Forexample, the first condensing lens 61 is configured as an aspheric lenshaving power mainly in the main scanning direction, and the lens surfaceshape is an aspheric surface expressed by a known function. The firstcondensing lens 61 is a convex meniscus, the power of which in the mainscanning section is larger than its power in the sub-scanning section,the main scanning section of which is not an arc, and which has aconcave surface facing the deflection unit 5. In addition, the shapewithin the main scanning section is symmetric with respect to theoptical axis. With respect to the sub-scanning direction, approximatelynon-power, that is, the incident surface and the emission surface havingthe same curvature, can be adopted, or power can be assigned accordingto specifications.

The second condensing lens 62 is an anamorphic lens having power mainlyin the sub-scanning direction, and the lens surface shape is an asphericshape expressed by a known function. That is, the second condensing lens62 is shaped so that its power within the sub-scanning section is largerthan the power within the main scanning direction, the incident surfaceof the main scanning section is an arc, and the other surface is not anarc. The shape within the main scanning section is symmetric withrespect to the optical axis, and the main scanning direction near theaxis is approximately non-power.

The shape of the sub-scanning section is as follows: the curvature ofthe incident surface is extremely gentle, that is, approximately planar,and the curvature of the emission surface gradually changes from theaxis to the outside of the axis, resulting in a convex shape which issymmetric with respect to the optical axis. The second condensing lens62 is, with respect to the incident light flux, in charge of condensingmainly in the sub-scanning direction and correction of minor distortionin the main scanning direction. The condensing relationship in thesub-scanning direction by the condensing lens system 6 constitutes aso-called tilt correcting system, where the reflective deflectionsurface 51 and the scanned surface 8 are in a conjugated relationship.

The cover glass 7 is inclined to have an angle with respect to theincident light flux within the sub-scanning section. This is for thepurpose of preventing light, which is reflected at the surface of thecover glass 7, from returning to the laser light source 1. If lightreflected at the surface returns to the laser light source 1, laseroscillation becomes unstable, varying the quantity of light.

In addition, the condensing lens system 6 is not necessarily configuredas described above, and the function expression formula can also be aknown expression formula. It can also be asymmetric with respect to theoptical axis, in order to improve condensing performance.

Synchronous Detection System

A synchronous detection reflection mirror (BD mirror) 9, which is asynchronous detection reflection optical unit, and synchronous detectioncondensing lens (BD lens) 10 are provided as a synchronous detectionoptical system, and, together with a synchronous detectionlight-receiving element (BD sensor) 11, constitute a synchronousdetection system. With respect to a light flux of an image heightoutside the effective image area on the scanned surface 8, the lightpath is divided by the BD mirror 9, and synchronous detection light isintroduced into the BD sensor 11 by the BD lens 10, so that timing ofprinting/writing is detected. As illustrated in FIG. 1A, a synchronousdetection light flux directed to the sensor surface passes through thecondensing lens 61, which constitutes a part of the condensing opticalsystem 6.

In FIGS. 1A and 1B, a most off-axis light flux 20 of the effective imagearea and a synchronous detection light flux 21 are illustrated. The mostoff-axis light flux 20 and the synchronous detection light flux 21 arebeams that scan in the direction of arrow A3 in FIG. 1B by rotation ofthe deflection unit 5. The most off-axis light flux 20 and thesynchronous detection light flux 21 are light paths at close timing, andthe BD mirror 9 separates a light flux directed to the BD sensor 11,which is a synchronous sensor, from a light flux directed to the scannedsurface.

The BD lens 10 at least has power in the main scanning direction, and isconfigured to condense a synchronous detection light flux 22, which isyet to pass through the BD lens 10, in the main scanning direction. TheBD sensor 11 has a light-receiving portion arranged near the mainscanning direction condensing point of the synchronous detection lightflux, and the light-receiving portion has an edge parallel with thesub-scanning direction. Alternatively, a BD edge member having an edgeparallel with the sub-scanning direction, which is provided towards thedeflection unit 5 from the light-receiving portion, is arranged near themain scanning direction condensing point of the synchronous detectionlight flux.

Methods for synchronous detection of a plurality of beams (multi-beam)include a method of synchronously detecting all of the plurality ofbeams and determining the write timing. According to another methodknown in the art, a specific beam is solely detected synchronously, andthe write timing of the other beams is determined by adding apredetermined delay time to the synchronously detected beam.

The most off-axis light flux 20 and the synchronous detection light flux21 are positioned as close as possible. This is because separationbetween the most off-axis light flux 20 and the synchronous detectionlight flux 21 requires increase of the effective area of the condensinglens 61 and increase of the reflective deflection surface 51 of thedeflection unit 5, making the apparatus larger.

BD Mirror

Next, the configuration of the BD mirror 9 as a synchronous detectionreflection optical unit will be described with reference to FIG. 1B. Inconnection with the BD mirror 9, as the distance between mirror endportion 921 and the effective reflection area is shorter, the apparatusis more effectively prevented from being larger. As described above,however, it is desired to solve the problem of corrosion of the endportion reflection area of the BD mirror 9 due to the influence oftemperature rise or humidity inside the image forming apparatus. Thiswill be described later in connection with a method for manufacturingthe BD mirror.

In FIG. 1B, the BD mirror 9 has first end surfaces 911 and 912 parallelwith the main scanning direction (arrow A3) and second end surfaces 921and 922 parallel with a direction (sub-scanning direction) perpendicularto the scanning direction (arrow A3). The first and second end surfacesare respectively two surfaces facing each other. The first end surfacesare preferably parallel with the main scanning direction, but are notnecessarily parallel with the main scanning direction (they can bearranged along the main scanning direction to have an angle of about 0to 10 degrees with respect to the main scanning direction).

Similarly, the second end surfaces are preferably parallel with thesub-scanning direction, but are not necessarily parallel with thesub-scanning direction (they can be arranged along the sub-scanningdirection to have an angle of about 0 to 10 degrees with respect to thesub-scanning direction).

The first and second end surfaces are preferably perpendicular to thereflection surface, and the first end surfaces have an area larger thanthat of the second end surfaces. Such a relative area determination ismade based on the following consideration: the BD mirror (reflectionmember), which has the reflection surface, the first end surfaces, andthe second end surfaces, is preferably a cuboid as a stereoscopic shape,but is not necessarily a cuboid. That is, at least one of the reflectionsurface, the first end surfaces, and the second end surfaces can have asurface shape deformed slightly from a rectangle, such as aparallelogram or a trapezoid. In such a case of deformation from thecuboid, the above-mentioned relative area determination can be madeassuming that a cuboid has not deformed.

Specifically, when the reflection surface has a shape deformed from arectangle, the above-mentioned relative area determination can be madeassuming that the reflection surface has a rectangular shape surroundedby a pair of straight lines inscribed in the shape of the reflectionsurface and parallel with the main scanning direction and another pairof straight lines parallel with the sub-scanning direction.

The specific size of the BD mirror 9 is as follows: the first endsurface 911 has a length of L1=11 mm, and the second end surface 921 hasa length of L2=10 mm, forming a rectangular shape. Since the first endsurfaces have an area larger than that of the second end surfaces asdescribed above, the first end surface 911 parallel with arrow A3 andthe second end surface 921 parallel with a direction perpendicular toarrow A3 have end edges of different lengths. This makes it possible torecognize the direction.

Method for Manufacturing the BD Mirror

Next, a first method for manufacturing the BD mirror 9 will be describedwith reference to FIGS. 2A to 2C. A process of preparing apre-deposition glass preform will be described with reference to FIG.2A. A float glass plate 930 (first optical member piece), which is areflection optical substrate as a preform of the BD mirror 9, has thefollowing size: its transverse end surface 933 has a length L1 of 11 mm,and the longitudinal end surface 934 has a length L3 of L3=L2×N+α.Taking any lengths as long as N is an integer and α is α<L2, the amountof discarded material can be reduced.

The float glass plate 930 is obtained by cutting large-size blank glassinto an elongated size of L3 mm in the longitudinal direction, whichcorresponds to the first cutting direction, and L1 mm in the transversedirection, which corresponds to the second cutting direction (firstprocess). The cutting is known scribe cutting. That is, the front orrear surface is scratched by a diamond blade along a line to be cut, andbending stress is applied to left and right sides of the line to be cut,so that the glass plate, to which stress is applied, is split along theline scratched by the diamond blade and then divided.

The scribe-cut section is generally susceptible to burring, so that thecut surface or its angled portion can be grinded or light-chamfered.Particularly, the longitudinal end surface 934 is preferablylight-chamfered to prevent any work-related injury.

Next, a process of forming a reflection coating on a surface of thefloat glass plate 930, which becomes a reflection optical surface,(second process) will be described with reference to FIG. 2B. FIG. 2Billustrates an elongated mirror 931 obtained by forming a multilayeredfilm 932 on the float glass plate 930 of an elongated size (thelongitudinal direction is brought into coincidence with a directionperpendicular to the main scanning direction). The surface of the floatglass plate 930 as a preform is cleaned and dried sufficiently, and avacuum deposition machine is used to form a group of films of at leasttwo types, including a metal reflection thin film and an overlyingprotection thin film, as a reflection coating.

The metal reflection thin film is formed using a metal-based material,specifically an aluminum-based material or a chromium-based material,when the cost is considered important, or a copper-based material whenexcellent reflection/no polarization characteristics are consideredimportant.

The protection thin film is formed as a single-layered or multilayeredfilm using a Ti-based material or a SI-based material for the purpose ofimproving resistance to moisture, resistance to wear, resistance tochemicals, resistance to oxidation, and the like. It is also possible toform an undercoat layer for the purpose of improving adhesion betweenthe metal reflection thin film and the glass preform. Such a reflectioncoating can be formed, instead of the above-mentioned vacuum deposition,by a coating technique such as sputtering.

Setting the float glass plate 930 of an elongated size in a vacuumdeposition machine requires less effort than when a small-piece glassplate of L1×L2 is set, thereby reducing the cost. Furthermore, the floatglass plate 930 is heavier than the small-piece glass plate of L1×L2 andis less likely to be displaced by impact or vibration than thesmall-piece glass plate of L1×L2, making it possible to stably form auniform film inside the vacuum deposition machine.

Next, a cutting process to obtain a BD mirror (small-piece mirror) as asecond optical member piece (third process) will be described withreference to FIG. 2C. As in the case of the float glass plate 930,scribe cutting is performed to obtain L2=10 mm, but light-chamfering canbe performed after the cutting. A BD mirror 9 is obtained as a result.

The present manufacturing method has a difference in that the first endsurfaces 911 and 912 are cut after deposition, but the second endsurfaces 921 and 922 are cut before deposition. That is, the first endsurfaces 911 and 912 are surfaces left unchanged since cutting afterformation of a reflection coating on the reflection surface, and thesecond end surfaces 921 and 922 are surfaces left unchanged sincecutting before formation of the reflection coating.

The first end surfaces 911 and 912, which have been cut afterdeposition, (surfaces cut in the transverse direction which is parallelwith the main scanning direction) are curled up just like the endportion 965 of the deposition film at the time of post-cutting asillustrated in FIG. 5B. The end portion 965 of the deposition film,which has been curled up, can easily contact external air, includingmoisture and O₂, and the reflection coating of metallic coatingincluding aluminum or an aluminum-containing alloy undergoesoxidation/corrosion.

As a result of an experiment of leaving the first end surfaces 911 and912 in an atmosphere of constant temperature and high humidity, forexample, temperature of 70° C. and humidity of 90%, for twenty days,corrosion has proceeded about 0.8 to 1.2 mm from the mirror end surface.It has been confirmed that the corroded part has a greatly reducedreflection ratio, meaning that the reflection performance falls as aresult of constant-temperature high-humidity endurance. Therefore, aneffective area of a direction (sub-scanning direction) perpendicular tothe main scanning direction can be set on the inside at a distance of atleast 1.2 mm from the mirror end portion.

In this case, the positional relationship of the most off-axis lightflux 20 and the synchronous detection light flux 21 in the main scanningdirection is not affected even if the distance between the first endsurfaces 911 and 912, which face each other in a direction (longitudinaldirection) perpendicular to the main scanning direction, increases anumber of millimeters. That is, there is no need to enlarge thecondensing lens 61 or the deflection surface 51 of the deflection unit 5in the main scanning direction, and the apparatus size does not increaseeither.

In contrast, in the case of the second end surfaces 921 and 922 whichhave been cut before deposition, the deposition film remains firmlyattached to the glass plate. Therefore, there is no end portion 965 ofthe deposition film, which has been curled up, as illustrated in FIG.5C. As a result, the reflection coating of the metallic coating hardlyundergoes oxidation/corrosion and, when left in an atmosphere ofconstant temperature and high humidity, for example, temperature of 70°C. and humidity of 90%, for twenty days, no corrosion has been observed,and the same reflection ratio characteristics as in the initial periodhave been obtained.

As a result, the second end surfaces 921 and 922, through which a lightflux deflected in the main scanning direction passes, require noconsideration of degradation of the reflection coating due to corrosion,making it possible to set a small effective area from the mirror endsurface. Specifically, light-chamfering provided on the longitudinal endsurface 934 of the float glass plate 930 is generally about C0.2 to 0.5,so that the distance between the mirror end surface and the effectivearea can be set to be about 0.6 mm.

As described above, the second end surfaces 921 and 922, which have beencut before deposition, hardly undergo corrosion (resistance to corrosionis excellent) compared with the first end surfaces 911 and 912. Thismakes it possible to reduce the distance between the mirror end surfaceand the effective area, in connection with the second end surfaces 921and 922, and to position the most off-axis light flux 20 and thesynchronous detection light flux 21 close to each other, thereby makingthe apparatus compact.

Furthermore, by employing a process of cutting the first end surfaces911 and 912 after deposition, deposition can be performed with respectto the float glass plate 930 of an elongated size, which reduces theeffort to set the substrate in the vacuum deposition machine, and whichdecreases the cost. Compared with a small-piece glass plate of L1×L2,the float glass plate 930 is hardly displaced by impact or vibration,making it possible to stably form a uniform film inside the vacuumdeposition machine.

The BD mirror 9 has the following size: mirror end portion 911 has alength L1=11 mm, and mirror end portion 912 has a length L2=10 mm, sothat it has a rectangular shape, with the end surfaces having differentlengths. Such different lengths make it possible to easily recognize endsurfaces that are resistant to corrosion. In addition, although arectangular shape of L1=11 mm, L2=10 mm has been described in connectionwith the present embodiment, the present invention is not limited tothis, and L1<L2 is also possible. Furthermore, a mounting standard canbe provided so that the mounting portions of the BD mirror correspond toL1 and L2, thereby preventing erroneous mounting.

Second Embodiment

Next, a second embodiment will be described with reference to FIGS. 3Ato 3D. As in the case of the first embodiment, the BD mirror 9 has firstend surfaces 911 and 912 parallel with the main scanning direction(arrow A3) and second end surfaces 921 and 922 parallel with a directionperpendicular to the main scanning direction (arrow A3). The size of theBD mirror 9 is as follows: the mirror end portion 911 has a length ofL1=11 mm, and the mirror end portion 921 has a length of L2=10 mm,forming a rectangular shape with end surfaces of different lengths.

Method for Manufacturing BD Mirror

Next, a second method for manufacturing the BD mirror 9 will bedescribed with reference to FIGS. 3A to 3D. FIG. 3A illustrates amedium-sized mirror before cutting. A float glass plate 941, which is aglass preform before deposition, has the following size: its length inthe main scanning direction (transverse direction) is L4=L1×M+β, and thelength in a direction (longitudinal direction) perpendicular to the mainscanning direction is L5=L2×N+α. Taking any lengths as long as M and Nare integers, α<L2, and β<L1, the amount of discarded material can bereduced.

The float glass plate 941 is obtained by cutting large-sized plate glassinto a desired medium size of L4 mm×L5 mm. The cutting is known scribecutting. That is, the front or rear surface is scratched by a diamondblade along a line to be cut, and bending stress is applied to left andright sides of the line to be cut. The glass plate, to which stress isapplied, is split along the line scratched by the diamond blade and thendivided. The scribe-cut section is generally susceptible to burring, sothat the cut surface or its angled portion can be grinded orlight-chamfered.

Next, a process of forming a reflection coating (first process) will bedescribed with reference to FIG. 3A. With respect to the float glassplate 941 as a preform, a surface, which becomes a reflection opticalsurface, is cleaned and dried sufficiently, and a vacuum depositionmachine is used to form a group of films of at least two types,including a metal reflection thin film and an overlying protection thinfilm, as a reflection coating. The metal reflection thin film is formedusing a metal-based material, specifically an aluminum-based material ora chromium-based material, when the cost is considered important, or acopper-based material when excellent reflection/no polarizationcharacteristics are considered important. The protection thin film isformed as a single-layered or multilayered film using a Ti-basedmaterial or a SI-based material for the purpose of improving resistanceto moisture, resistance to wear, resistance to chemicals, resistance tooxidation, and the like.

It is also possible to form an undercoat layer for the purpose ofimproving adhesion between the metal reflection thin film and the glasspreform. Such a coating can be formed, instead of vacuum deposition, bya coating technique such as sputtering. In this manner, a medium-sizedmirror 940 is manufactured by coating the float glass plate 941, whichis a reflection optical substrate, with a reflection coating 942.

Next, as illustrated in FIG. 3B, the medium-sized mirror 940 is cut intoa mirror 943 of an elongated size (second process). The above-mentionedscribe cutting is employed to obtain a dimension of L1 mm (transversedirection)×L5 mm (longitudinal direction). After the cutting,light-chamfering is preferably performed to prevent any work-relatedinjury.

The cut surface after formation of the reflection coating is curled upjust like the end portion 965 of the deposition film as illustrated inFIG. 5C. The end portion 965 of the deposition film, which has beencurled up, can easily contact external air, including moisture and O₂,and the reflection coating of metallic coating including aluminum or analuminum-containing alloy undergoes oxidation/corrosion. Particularly,corrosion proceeds rapidly in an atmosphere of high temperature and highhumidity. Therefore, corrosion of the cut surface is prevented in thefollowing process.

A process of applying a corrosion inhibitor (third process) will bedescribed with reference to FIG. 3C. A corrosion inhibitor 944 isapplied to a longitudinal end surface along a longitudinal end portionchamfered portion of the mirror 943 of an elongated size, which is afirst optical member piece cut from the medium-sized mirror 940. As thecorrosion inhibitor, trademark “MIRRORTECT” (NGS INTERIA CO., LTD.) isused, for example. Since application can be performed in a breath in anelongated state having a dimension of L1 mm×L5 mm, the number ofprocesses can be smaller than when application is performed with respectto a smaller dimension of L1 mm×L2 mm.

Next, a cutting process to obtain a small-piece BD mirror 9′ as a secondoptical member piece (fourth process) will be described with referenceto FIG. 3D. Scribe cutting is performed to obtain L2=10 mm.Light-chamfering can be performed after the cutting, and a BD mirror 9′is obtained in this manner.

In connection with the BD mirror 9′, there is a difference in that thefirst end surfaces 911 and 912 are left unchanged since cutting, while acorrosion inhibitor 944 has been applied to the second end surfaces 921and 922 after cutting. The first end surfaces 911 and 912 are curled upjust like the end portion 965 of the deposition film at the time ofpost-cutting, as illustrated in FIG. 5C. The end portion 965 of thedeposition film, which has been curled up, can easily contact externalair, including moisture and O₂, and the reflection coating of metalliccoating including aluminum or an aluminum-containing alloy undergoesoxidation/corrosion.

Particularly, corrosion proceeds rapidly in an atmosphere of hightemperature and high humidity, and, as a result of an experiment ofleaving the first end surfaces 911 and 912 in an atmosphere of constanttemperature and high humidity, for example, temperature of 70° C. andhumidity of 90%, for twenty days, corrosion has proceeded about 0.8 to1.2 mm from the mirror end surface. It has been confirmed that thecorroded part has a greatly reduced reflection ratio, meaning that thereflection performance falls as a result of constant-temperaturehigh-humidity endurance. Therefore, an effective area can be set on theinside at a distance of at least 1.2 mm from the mirror end portion.However, the positional relationship of the most off-axis light flux 20and the synchronous detection light flux 21 is not affected even if thedistance between the first end surfaces 911 and 912 increases a numberof millimeters, there is no need to enlarge the condensing lens 61 orthe deflection surface 51 of the deflection unit 5, and the apparatussize does not increase either.

In contrast, in the case of the second end surfaces 921 and 922 to whicha corrosion inhibitor 944 has been applied, the reflection coating ofmetallic coating hardly undergoes oxidation/corrosion, due toapplication of the corrosion inhibitor. When left in an atmosphere ofconstant temperature and high humidity, for example, temperature of 70°C. and humidity of 90%, for twenty days, no corrosion has been observed,and the same reflection ratio characteristics as in the initial periodhave been obtained. As a result, the second end surfaces 921 and 922require no consideration of degradation of the reflection coating due tocorrosion, making it possible to set a small effective area from themirror end surface. Specifically, light-chamfering provided on thelongitudinal end surface 934 of the float glass plate 930 is generallyabout C0.2 to 0.5. Thus, the distance between the mirror end surface andthe effective area can be set to be about 0.6 to 0.7 mm.

As described above, the second end surfaces 921 and 922, which have beencut before deposition, hardly undergo corrosion (resistance to corrosionis excellent) compared with the first end surfaces 911 and 912. Thismakes it possible to reduce the distance between the mirror end surfaceand the effective area, in connection with the second end surfaces 921and 922, and to position the most off-axis light flux 20 and thesynchronous detection light flux 21 close to each other, thereby makingthe apparatus compact in the main scanning direction.

Furthermore, by employing a process of cutting the medium-sized mirror940 into a size of L1×L5 after deposition, the effort to set thesubstrate in the vacuum deposition machine can be saved, and the costcan be reduced. Compared with a small-piece glass plate of L1×L2, themedium-sized mirror 940 is hardly displaced by impact or vibration,making it possible to stably form a uniform film inside the vacuumdeposition machine. In addition, although a rectangular shape of L1=11mm, L2=10 mm has been described in connection with the presentembodiment, the present invention is not limited to this.

Modification 1

Although it has been assumed in the above description of an embodimentthat the light source has a plurality light-emitting portions so that aplurality of light fluxes (multi-beam) passes through a synchronousdetection reflection optical unit, the light source can also have asingle light-emitting portion so that a single light flux (single beam)passes through the synchronous detection reflection optical unit.

Modification 2

In addition, although a synchronous detection mirror has beenillustrated as a synchronous detection reflection optical unit, themirror can be replaced with a prism, for example.

Modification 3

The above-described embodiment has adopted a so-called monolithicmulti-beam scheme, where a plurality of light-emitting points isprovided on a single semiconductor substrate, as a light source typeused in a multi-beam scanning system. According to this scheme, no beamcomposition unit is necessary if the semiconductor laser element canalso be manufactured, so that use of such a light source element makesthe scanning optical apparatus simple and easily makes the entireapparatus compact. However, it is also possible to arrange a pluralityof semiconductor laser elements, which emit laser light (light flux), intandem, as another light source type, and to obtain a plurality of lightfluxes using a light path composition unit of a polarization beamsplitter or a half mirror.

In addition, semiconductor laser elements employing a monolithicmulti-beam scheme are largely classified into two groups. The firstgroup includes horizontal resonator-type semiconductor lasers, and thesecond group includes vertical resonator-type semiconductor lasers. Suchsemiconductor laser elements are classified according to whether thedirection of the resonator (light beam emission direction) is parallelor vertical with respect to the configuration of elements stacked on thewafer substrate surface, although either group of them are manufacturedby a semiconductor process.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2012-270305, filed on Dec. 11, 2012, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A scanning optical apparatus comprising: adeflection unit configured to deflect a light flux from a light sourcein a main scanning direction; an incident optical system (2, 3, 4)configured to introduce the light flux from the light source to thedeflection unit; a condensing optical system (6) configured to condensethe light flux from the deflection unit onto a scanned surface; and areflection member (9) arranged in a light path of the light fluxdeflected in the main scanning direction by the deflection unit andconfigured to reflect a part of the deflected light flux, wherein thereflection member has a reflection surface configured to reflect thedeflected light flux, a first end surface formed in the main scanningdirection, and a second end surface formed in a sub-scanning directionperpendicular to the main scanning direction, and the second end surfacehas a higher degree of corrosion resistance than the first end surface.2. The scanning optical apparatus according to claim 1, wherein thefirst end surface is a surface left unchanged since cutting afterformation of a reflection coating on the reflection surface, and thesecond end surface is a surface left unchanged since cutting beforeformation of the reflection coating.
 3. The scanning optical apparatusaccording to claim 1, wherein the first end surface is a surface leftunchanged since cutting, and the second end surface is a surface coatedwith a corrosion inhibitor.
 4. The scanning optical apparatus accordingto claim 1, wherein a length of the reflection surface of the reflectionmember in the main scanning direction is different from a length of thereflection surface of the reflection member in the sub-scanningdirection.
 5. The scanning optical apparatus according to claim 4,wherein a length of the reflection surface of the reflection member inthe main scanning direction is larger than a length of the reflectionsurface of the reflection member in the sub-scanning direction.
 6. Thescanning optical apparatus according to claim 1, wherein the reflectionmember is a part of a synchronous detection unit and is configured toseparate a light flux directed to a sensor surface as a synchronousdetection light flux from the light flux directed to the scannedsurface.
 7. The scanning optical apparatus according to claim 1, whereinthe light flux deflected in the main scanning direction passes through aplane including the second end surface.
 8. The scanning opticalapparatus according to claim 1, wherein the reflection member is amember obtained by cutting a mirror, which is provided with a reflectioncoating, along at least one cut surface parallel with a transversedirection, and a pre-cutting longitudinal direction of the mirrorcoincides with the sub-scanning direction.
 9. The scanning opticalapparatus according to claim 1, wherein the reflection member is amember obtained by cutting a mirror, which is provided with a reflectioncoating on a surface corresponding to the reflection surface, along atleast one cut surface parallel with a transverse direction of themirror, without cutting the mirror in a direction parallel with alongitudinal direction of the mirror, and a pre-cutting longitudinaldirection of the mirror is parallel with the sub-scanning direction, anda pre-cutting transverse direction of the mirror is parallel with themain scanning direction.
 10. The scanning optical apparatus according toclaim 1, wherein the light flux deflected in the main scanning directionis a plurality of light fluxes.
 11. An image forming apparatuscomprising: the scanning optical apparatus according to claim 1; aphotosensitive body arranged on the scanned surface; a developing unitconfigured to develop, as a toner image, an electrostatic latent imageformed on the photosensitive body by the light flux deflected by thescanning optical apparatus; a transferring unit configured to transferthe developed toner image to a transferred material; and a fixing unitconfigured to fix the transferred toner image to the transferredmaterial.
 12. An image forming apparatus comprising: the scanningoptical apparatus according to claim 1; and a printer controllerconfigured to convert code data input from an external apparatus into animage signal and input the image signal to the scanning opticalapparatus.
 13. A method for manufacturing a reflection member of ascanning optical apparatus including: a deflection unit configured todeflect a light flux from a light source in a main scanning direction;an incident optical system (2, 3, 4) configured to introduce the lightflux from the light source to the deflection unit; a condensing opticalsystem (6) configured to condense the light flux from the deflectionunit onto a scanned surface; and a reflection member (9) arranged in alight path of the light flux deflected in the main scanning direction bythe deflection unit and configured to reflect a part of the deflectedlight flux, the method comprising: cutting a reflection opticalsubstrate in a first cutting direction corresponding to a directionparallel with a sub-scanning direction perpendicular to the mainscanning direction and obtaining a first optical member piece (930) of arectangular shape elongated in the first cutting direction; forming areflection coating on a reflection optical surface of the first opticalmember piece (930); and cutting the first optical member piece (930) ina second cutting direction corresponding to a direction parallel withthe main scanning direction and obtaining a second optical member piece(9′) as the reflection member.
 14. A method for manufacturing a scanningoptical apparatus including: a deflection unit configured to deflect alight flux from a light source in a main scanning direction; an incidentoptical system (2, 3, 4) configured to introduce the light flux from thelight source to the deflection unit; a condensing optical system (6)configured to condense the light flux from the deflection unit onto ascanned surface; and a reflection member (9) arranged in a light path ofthe light flux deflected in the main scanning direction by thedeflection unit and configured to reflect a part of the deflected lightflux, the method comprising: cutting a reflection optical substrate in afirst cutting direction corresponding to a direction parallel with asub-scanning direction perpendicular to the main scanning direction andobtaining a first optical member piece (930) of a rectangular shapeelongated in the first cutting direction; forming a reflection coatingon a reflection optical surface of the first optical member piece (930);cutting the first optical member piece (930) in a second cuttingdirection corresponding to a direction parallel with the main scanningdirection and obtaining a second optical member piece (9′) as thereflection member; and embedding the second optical member piece in ahousing of the scanning optical apparatus.
 15. A method formanufacturing a reflection member of a scanning optical apparatusincluding: a deflection unit configured to deflect a light flux from alight source in a main scanning direction; an incident optical system(2, 3, 4) configured to introduce the light flux from the light sourceto the deflection unit; a condensing optical system (6) configured tocondense the light flux from the deflection unit onto a scanned surface;and a reflection member (9) arranged in a light path of the light fluxdeflected in the main scanning direction by the deflection unit andconfigured to reflect a part of the deflected light flux, the methodcomprising: forming a reflection coating (942) on a reflection opticalsurface of a reflection optical substrate (941); cutting the reflectionoptical substrate (941), on which the reflection coating has beenformed, in a first cutting direction corresponding to a directionparallel with a sub-scanning direction perpendicular to the mainscanning direction and obtaining a first optical member piece (943) of arectangular shape elongated in the first cutting direction; applying acorrosion inhibitor to an end surface (944) of the first optical memberpiece (943) cut in the first cutting direction; and cutting the firstoptical member piece (943) in a second cutting direction correspondingto a direction parallel with the main scanning direction and obtaining asecond optical member piece (9′) as the reflection member.
 16. A methodfor manufacturing a scanning optical apparatus including: a deflectionunit configured to deflect a light flux from a light source in a mainscanning direction; an incident optical system (2, 3, 4) configured tointroduce the light flux from the light source to the deflection unit; acondensing optical system (6) configured to condense the light flux fromthe deflection unit onto a scanned surface; and a reflection member (9)arranged in a light path of the light flux deflected in the mainscanning direction by the deflection unit and configured to reflect apart of the deflected light flux, the method comprising: forming areflection coating (942) on a reflection optical surface of a reflectionoptical substrate (941); cutting the reflection optical substrate (941),on which the reflection coating has been formed, in a first cuttingdirection corresponding to a direction parallel with a sub-scanningdirection perpendicular to the main scanning direction and obtaining afirst optical member piece (943) of a rectangular shape elongated in thefirst cutting direction; applying a corrosion inhibitor to an endsurface (944) of the first optical member piece (943) cut in the firstcutting direction; cutting the first optical member piece (943) in asecond cutting direction corresponding to a direction parallel with themain scanning direction and obtaining a second optical member piece (9′)as the reflection member; and embedding the second optical member piecein a housing of the scanning optical apparatus.
 17. The method accordingto claim 13, wherein formation of the reflection coating is performed byvacuum deposition or sputtering.